An altered state of consciousness (ASC),[1] also called altered state of mind, is any condition which is significantly different from a normal waking beta wave state. The expression was used as early as 1966 by Arnold M. Ludwig[2] and brought into common usage from 1969 by Charles Tart.[3][4] It describes induced changes in one's mental state, almost always temporary. A synonymous phrase is "altered state of awareness".

Altered states of consciousness can be associated with artistic creativity[5] or different focus levels. They also can be shared interpersonally and studied as a subject of sociological research.[6]

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During an altered state of consciousness, brain waves occupy different categories of frequencies (i.e. Epsilon, Delta, Theta, Alpha, Beta, Gamma). These waves can be measured using an Electroencephalograph (EEG). Below is a list of wave types, along with their corresponding frequencies and states of consciousness:

As the ability to measure brainwave frequency has significantly improved with advances in digital technology, it has become possible and practical to measure brainwave frequencies beyond 30 Hz. As more is learned about these brainwaves, a change in classifications may occur. The beta-wave level of consciousness seems to extend well beyond 30 Hz, but frequencies of 90 Hz or more (gamma waves), are shown to be associated with coordination of signals across longer distances within the brain, facilitating the completion of complex actions or associations which require the simultaneous use of multiple brain regions.